Perforations or "perfs" are generally
classified for print specifications in one of two ways: 1) bursting strength
or 2) TPI, which is commonly called either "Ties Per Inch" or "Teeth
Per Inch".

Burst and Tear Strength

Burst strength is a measurement of the pressure (as measured on a burst strength
gauge) that is required to detach the perforated section of a document. Tear strength is the physical effort necessary for removal
of the perforated section. Tear strength can be categorized as "light
release" which is easily torn, "medium release" which gives
moderate resistance to removal, or "stiff release" which provides
the greatest resistance from repeated handling and attempted removal.

The purpose and function of the
perforated section often determines whether the perforation is to be an easy release
variety (3 to 6 TPI) or a stiffer release (10 to 18 TPI). The weight of the
stock combined with the TPI will also affect the burst strength.

Teeth per inch or ties per inch are both approximately the same count, but
not the same dimensions. The tie or tab is the part of the perforation where
the paper does not get cut, but remains intact to "tie" the paper
together. The ties, or uncut areas, alternate with cut areas to form the perforation.
The tied areas of the perforation are usually shorter in width than the cut
areas in order to allow for easier detachment of the sections separated by
the perforation.

Application Methods

Products Printed and Perforated Online (Web Presses)

When a perforation must be applied parallel to the direction that the paper
travels through the printing press, a steel segmented wheel is used. The segmented
wheel rolls along the paper and applies the required cuts per inch as the
paper is pulled through the press. Multiple perforations can be applied at
the same time.

For perforations that must be perpendicular to the direction the paper travels
through the printing press, steel perforation rules are used, which are inserted
into cylinders on the press. As the cylinders revolve, the perforations are
cut into the paper. More than one perpendicular perforation may be applied
at one time, but the print supplier may be much more limited in the number
and position of perpendicular perfs that can be applied at one time as compared
to the number and positions of parallel perforations. Both parallel and perpendicular
perforations can be applied at the same time.

Printed Products Perforated Offline

There are occasions when perforations are added as an offline process, after
the product has been printed. Generally, products that have a perforation
applied offline are for smaller quantities and have been printed on sheet
fed presses. Large quantities are more economical to print and perf in one
operation at a web press. Many products that are perfed offline are sent through
equipment that can apply only full-length perforations and use wheels similar
to those used on a web press. The perforating wheels apply full perforations
either parallel or perpendicular to the grain of the paper, depending on the
direction the paper is sent through the equipment. To apply both parallel
and perpendicular perforations, the paper is sent through the equipment twice.
To help save time, some products can be manufactured with several printed
copies on one large sheet so that when the sheet is sent through the perfing
equipment, the perforations are applied to all of the copies on the large
sheet at the same time. The large sheets are then cut into individual finished
pieces.

Perforations that are more complicated, such as a perforation that borders
a detachable business card or a rolodex card within a larger sheet, can be
applied with a perf cutting method, which is accomplished much the same as
die cutting.
Perforating blades, which contain cut and uncut areas, are constructed into
a pattern. The cut area of the blade strikes through the material while the
uncut segment or tie of the blade does not cut the paper, enabling the perforated
area to remain attached to the document until it is to be removed.

Perforation Direction Designation

Parallel Perforation:

Perpendicular Perforation:

Parallel perforations run in the same direction that the paper
travels through the press.

The number and position of the perforations is usually not critical
for full parallel perforations.

Partial perforations do not run the full size of the printed piece.

The number and position of partial perforations are limited. Consult
your supplier for information on these limitations.

Perpendicular perforations run in the opposite direction that
the paper travels through the press.

There are limitations on the number and position of perforations
allowed.

Partial perpendicular perforations do not run the full size of
the printed piece.

The number and position of partial perforations are limited. Consult
your supplier for information on these limitations.

Selecting the Proper TPI

There may be special requirements that should be considered for the
perforation, such as the repeated or excessive handling of the perforated
stock.

Outline any additional processing that will be required on the paper stock
such as imprinting or folding, and how the end user will detach the perforated
section.

Consider the function of the perforation such as folding or bursting (folding enables the document to fit into an envelope).

The coating on the stock, which can cause the perforation to become lighter in depth
than what was anticipated and less likely to detach as desired unless this factor
is considered.

Consider the bursting strength that is required and the tear strength desired.

Perforation Selection Chart

The following perforation patterns are general
representations of the cut and uncut dimensions of the perforation. The length
of the cut and uncut sections can be shorter or longer depending on special
requirements of the perforated product. The patterns shown are merely standard
dimensions and can be changed if necessary.

3 to 4 TPI: When one section of a document needs to detach easily
from another section, 3 and 4 tie perforations are good choices. They are not recommended
for a sheet that must remain intact for long periods of time because the ties
are too loose.

5 to 6 TPI: Because there are more ties per inch, 5 and 6 tie perforations
are stronger than the 4 TPI, but they are still too loose to be used for documents
that must remain intact for long periods of time.

7 to 10 TPI: 7 TPI through 10 TPI perforations are stronger than
the 4 or 6 TPI and help to keep the document intact until it is ready to be
detached. They are most often used as a perforation within the document that allows
the user to remove a section of the document.

11 to 14 TPI: The 11 to 14 TPI category is also referred to as a
"statement perf". They are most often used as a perf within a document that allows the user to remove a section of the document. For example,
the top or bottom section of a "statement of account" form may be
detached and sent back with a payment. The perforations are durable so it is best to fold the perforated section to weaken the perforation allowing for easier detachment.

16 to 17 TPI: 16 and 17 TPI are stronger than the statement perforations and must
be folded to weaken the perforation so that it detaches more easily. They
are often used on magazine inserts and mailers.

Letteredge or Invisible Perf: As the name implies, this perf is nearly
invisible and leaves a clean, smooth edge after the perforation is detached. The
most common ties per inch for letterhead perfs are 50, 66, and 72. Most print
providers use one of these ties per inch as the standard for all of their
letteredge perfs unless a specific TPI is requested. A letteredge perforation
does not work well on paper stock heavier than 24 lb. bond because
it is too difficult to control the depth of the perforation. Using a stock
that is too heavy in weight may result in a perforation that does not detach
properly. If you are unsure of which TPI to use, you should discuss the options
with your print supplier.

Samples of Perforations

Print materials can contain multiple perforations
enabling a variety of tasks to be accomplished for additional processing of
the document.

Note: Always check with the supplier of the
product to insure that the required perforation can be accomplished
on the material desired and in the location or locations indicated.